KR19990021186A - Method and apparatus for driving brushless three-phase DC motor - Google Patents

Abstract

The present disclosure relates to a method and apparatus for driving a brushless three-phase DC motor for driving a brushless three-phase DC motor without a rotational position sensor from a stationary state to a sensorless mode. The driving method of the present invention comprises the steps of exciting two phases of a brushless three-phase DC motor in a stationary state, applying an energization signal for exciting two phases 120 degrees ahead of the two excited phases; And a step of switching to the sensorless mode at the same time, and including a driving device for controlling each driving step. Therefore, the present invention does not need to know the position of the rotor by the counter electromotive force, the driving method is simple, as well as to prevent the overcurrent by the conventional forced driving, thereby providing the effect of reducing the driving power and protecting the motor. In addition, the present invention can be applied to various products using a brushless DC motor, such as a washing machine, an air conditioner, a refrigerator, a VCR, and an automobile.

Description

Method and apparatus for driving brushless three-phase DC motor

The present invention relates to a brushless three-phase DC motor, and more particularly, to a brushless three-phase DC motor driving method for driving the brushless three-phase DC motor in a stationary state to rotate at a constant speed and the same. It relates to a driving device for controlling.

Typical DC motors use a built-in brush and commutator to rotate the motor. In contrast, a brushless three-phase DC motor refers to a motor that controls and rotates gate voltages of transistors (hereinafter, TR) and field effect transistors (hereinafter, MOSFETs) constituting a driving circuit by a computer. In addition, the brushless three-phase DC motor has the advantage that the brush wear and the commutation of the commutator generated in a general DC motor is removed.

An apparatus and method for driving such a conventional brushless three-phase DC motor is illustrated in FIGS. 1, 2, and 3.

1 is a block diagram showing a driving apparatus of a conventional brushless three-phase DC motor.

As shown in FIG. 1, the conventional driving apparatus includes a power supply unit 10 for applying power to operate the three-phase DC motor 30, and at the output end of the power supply unit 10, a three-phase DC motor ( An inverter 20 for driving 30 is connected. The inverter 20 is coupled to the three-phase DC motor 30 is driven by receiving the voltage output from the inverter 20. Then, the control unit 40 for controlling the rotation state of the brushless three-phase DC motor 30 is connected to the inverter 20 and the DC motor 30, the operator 40 is operated by the operator to control the system The control unit 50 is connected.

The A / D converter 401 of the control unit 40 inputs a zero-cross pulse (signal for position detection, hereinafter referred to as ZCP) from one other line except for two-phase signal lines for supplying a driving voltage to the DC motor 30. Receive it and convert it into a digital signal for output. A positioning end 402 for determining the position of the rotor is connected to the output end of the A / D converter 401. The output of the positioning stage 402 is connected to the delay calculating stage 403 and the speed calculating stage 404, respectively.

In addition, the operation control unit 50 generates a rotational speed signal of the DC motor 30 adjusted by the operator, which is input to the subtractor 405 via the A / D converter 406. The subtractor 405 receives the outputs of the A / D converter 406 and the speed calculator 404 of the controller 40 connected to the operating control unit 50, and proportionally integrates the signal corresponding to the difference 407. To feed. The output of the proportional integral stage 407 is applied to the PWM conversion stage 408. The PWM conversion stage 408 is selectively connected to the open-loop driver 409 and the delay calculation stage 403 according to the operation mode, and applies the final output of the control unit 40 to the inverter 20.

Each stage in the controller 40 has a connected structure in which inputs and outputs are transmitted in a constant direction, whereas the open-loop driver 409 exists independently. When the DC motor 30 is in the stopped state, the open-loop driver 409 forcibly drives the DC motor 30 before switching to the sensorless mode.

2 is a block diagram showing an inverter and a three-phase DC motor of the brushless three-phase DC motor driving device in an equivalent circuit.

As shown, the inverter 20 and the three-phase DC motor 30,

An input voltage Vd for operating the circuit, three phase drive circuits 20a, 20b, 20c for driving three phases of the DC motor 30, and a three-phase DC motor 30 are included. Each of the phase driving circuits 20a, 20b, and 20c has a TR and a diode coupled in parallel, and two such parallel pairs are connected in series. The three-phase DC motor 30 has a Y connection, and each phase includes a resistor R, an excitation coil L, and an electromagnet Ea, Eb, and Ec.

FIG. 3 illustrates a model of a control pulse applied to each gate of a three-phase drive circuit in an inverter during open-loop forced driving.

As shown, the duty of the open-loop forced drive pulse (the ratio of the high and low states of the pulse signal) has six different states, and the duty takes the form of changing from a small value to a large value.

The operation of the brushless three-phase DC motor according to the conventional invention will be described in detail with reference to FIGS. 1, 2, and 3.

The conventional brushless three-phase DC motor 30 operates in two modes, namely, the open-loop driving mode from the standstill to the sensorless mode, and the rotation of the DC motor 30 during the open-loop driving. When this constant speed is reached, it is divided into sensorless mode.

First, referring to FIG. 1, a sensorless mode that is a general rotation state of a motor will be described.

As shown, the DC power applied from the power supply unit 10 is supplied to the inverter 20. The inverter 20 includes a phase driving circuit for driving three phases embedded in the DC motor 30, and a signal for controlling the three phases is supplied from the PWM conversion stage 408 of the controller 40.

The inverter has three TRs of three phase driving circuits (see FIG. 2), and the PWM conversion stage 408 outputs driving signals to six control signal lines connected to the gates of the six TRs.

For example, when a gate voltage is applied to the first two TRs, Ta + and Tb-, the upper TR of the a phase driving circuit and the TR of the bottom of the b phase driving circuit are conducted so that the phases a and b of the DC motor 30 are connected. Become a woman. When these two phases are excited, the motor starts to rotate under the rotational driving force.

Next, when a gate voltage is applied to the two TRs, Tb + and Tc- at a short time interval, the upper end of the phase b driving circuit and the lower end of the phase c driving circuit are conducted so that the phases b and c of the DC motor 30 are connected. Become a woman.

This second control signal drives two phases 120 degrees ahead of the first two phases driven, and if the control signal is continuously applied while changing the phase in this manner, the DC motor 30 rotates. .

When the DC motor 30 rotates, the ZCP indicating the rotation position is input to the A / D converter 401 of the controller 40. ZCP is a signal by the counter electromotive force coming out of the remaining one phase in which no driving current flows. For example, if the phases a and b are operating by applying currents driving the phases a and b in the inverter 20 to the three-phase DC motor 30, the signal output by the counter electromotive force in the remaining phase c is ZCP. to be.

The ZCP input to the A / D converter 401 is converted into a digital signal, which is input to the positioning stage 402. In the positioning stage 402, the current position of the rotor is calculated and supplied to the delay calculating stage 403 and the speed calculating stage 404. Delay calculation stage 403 calculates the time to increase or decrease the pulse duty to meet the rotational speed specified by the operator.

The speed calculator 404 calculates the current speed and applies it to the subtractor 405. Another input of the subtractor 405 is applied from the operating control section 50. Operation control unit 50 is provided with a control panel for the operator to control the rotation state of the DC motor (30). When the operator steers at a desired rotational speed, that is, increases or decreases the rotation, the steering signal is converted into a digital signal by the A / D converter 406 and input to the subtractor 405.

The subtractor 405 compares the current speed of the DC motor 30 with the speed specified by the operator and applies a signal corresponding to the difference to the proportional integral 407. The proportional integrating stage 407 integrates the signal input from the subtractor 405 and supplies it to the PWM converting stage 408, and the PWM converting stage 408 is input from the delay calculating stage 403 and the proportional integrating stage 407. The gate control pulse calculated by the two signals to be outputted to the inverter 20.

Referring to Figures 2 and 3, let's look at the conventional open-loop forced drive method for driving the DC motor 30 in a stationary state. The conventional open-loop forced driving method is a conventional driving method of rotating the DC motor 30 before switching to the sensorless mode when the brushless three-phase DC motor 30 is stopped and no counter electromotive force can be generated.

The switch S.W of the controller 40 is switched to connect the open-loop driver 409 to the PWM conversion stage 408 (see FIG. 1). The open-loop driver 409 forcibly generates open-loop drive pulses having six states, as shown in FIG. At this time, the open-loop driver 409 unilaterally changes the PWM duty in proportion to the speed specified by the operator. This signal accelerates the rotation of the brushless three-phase DC motor 30 to a predetermined speed. The controller 40 starts sensing the terminal voltage at a speed having a PWM duty larger than the output signal of the delay calculation stage 403. The controller 40 detects the ZCP of the sensed terminal voltage, and switches to the sensorless mode when two consecutively detected ZCP intervals are similar to the intervals of the driving pulses applied in the open-loop forced driving.

However, in the conventional brushless three-phase DC motor driving method as described above, when the rotational acceleration of the DC motor and the duty of the forced driving pulse do not match to some extent, ZCP is not detected, so the sensorless mode is not easily switched. In addition, there is a problem in that an overcurrent flows because a large power pulse is applied for driving during open-loop forced driving.

Accordingly, it is an object of the present invention to provide a novel driving method and apparatus to solve the above problems.

1 is a block diagram showing a driving apparatus of a conventional brushless three-phase DC motor.

2 is an equivalent circuit of an inverter and a three-phase DC motor of a conventional driving device.

3 shows an example of a conventional open-loop forced drive pulse for driving a brushless three-phase DC motor.

Figure 4 is a simplified diagram of the equivalent circuit of the inverter and the three-phase DC motor of Figure 2 to explain the operation of the brushless three-phase DC motor.

5 is a view showing a method for driving a brushless three-phase DC motor according to the present invention.

Figure 6 is a block diagram showing a drive device for a brushless three-phase DC motor according to the present invention.

Explanation of symbols for main parts of the drawings

10: power supply 20: inverter

30: Brushless 3-phase DC Motor

30a; Phase a 30b: Phase b

30c: c phase 302: rotor

40: control unit

401, 406: A / D converter 402: Positioning stage

403: delay calculation stage 404: speed calculation stage

405: subtractor 407: proportional integral

408: PWM conversion stage 409: open-loop driver

50: operation control unit 60: initial drive unit

70: automatic changeover switch

T1: Open-loop forced drive time T2: Sensorless mode switching point

To drive the brushless three-phase DC motor according to the present invention for achieving the above object,

Exciting two phases of the stationary DC motor, giving an energization signal for exciting two phases 120 degrees ahead of the excited two phases, and switching to a sensorless mode upon application of the energization signal do.

In addition, the driving device of the present invention to perform the driving step,

A circuit for applying current to two phases, for example, phases a and b, a circuit for applying an energization signal to two phases 120 degrees ahead of the excited two phases, and a sensorless mode simultaneously with application of the energization signal. An initial drive part including a circuit for switching is included.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the sensorless drive device and method of a brushless three-phase DC motor according to the present invention.

4 is a simplified block diagram of an inverter of a brushless three-phase DC motor.

With reference to Figure 4, the brushless three-phase DC motor is developed to determine the rotational conditions for operating in the sensorless mode. In addition, the above equation development provides a basic concept for carrying out the present invention.

As shown, the solid arrows show the current i flowing in the circuit when the drive signal is applied to Ta + of the a-phase drive circuit and Tb- of the b-phase drive circuit. At this time, the C phase is open and generates counter electromotive force when the motor is operated in the sensorless mode.

When Ta + is on, the drive voltage of TR increases the main current i; when Ta + is off, current i flows down through the freewheeling diode Da-. At this time, the loop equation through Da- and Tb- is shown in Equation (1).

Summarizing the above equation, it is the same as Equation 2.

Meanwhile, the neutral point voltage v _n of the DC motor 30 is expressed by Equation 3 below.

Therefore, the neutral point voltage v _n is expressed as in Equation 4.

In addition, since the terminal voltage v _c of the C phase is e _c + v _n, it is represented by Equation 5.

Where v _ce is the forward voltage drop between the collector and emitter of the driving TR, and v _F is the forward voltage drop of the freewheeling diode. This equation is valid even when the DC motor 30 is in a transient state since resistance and inductance are considered in the induction process, but the constants related to the DC motor 30 are not included.

Since the energization condition of the diode D _C- is v _c -V _F , substituting the above equation is as in Equation 6.

Since the back EMF is trapezoidal, e _a + e _b is almost zero when the value e _c is near zero. Therefore, the energization condition of D _C- is given by Equation 7.

In general, V _ce and V _F are much smaller than the counter electromotive force, so when the counter electromotive force e _c on _c is negative, an open c phase current flows through the diode D _C- .

With reference to the above-described equation evolution, the operating conditions of the sensorless mode will be described in detail. The sensorless mode means that the DC motor 30 is rotated in a stable state. At this time, the controller can detect a ZCP indicating the rotation position. As described above, the ZCP is a signal due to the counter electromotive force coming out of one phase in which the three-phase driving current does not flow.

When the counter electromotive force is detected, the position of the rotor can be detected, so that it can be continuously rotated. In order to detect the counter electromotive force, the DC motor must be rotating at a constant speed or more.

Since the magnitude of the counter electromotive force is proportional to the speed of the rotor, it is impossible to detect the position of the rotor at rest. The energization condition of the freewheeling diode is as shown in Equation 7 above. Therefore, to detect the current in the open phase, the back EMF of the open phase must be greater than (V _CE + V _F ) / 2. Since V _CE + V _F is usually 1.2V, the counter electromotive force is 0.6V or more according to equation (7). Since the counter electromotive force constant of the DC motor 30 is large, the rotation speed that can inversely detect the counter electromotive force is small. For example, when the back EMF constant K _v is 27.7 μs / rpm, the speed capable of detecting 0.6 _V is 22 rpm. In conclusion, in the above case, in order to switch to the sensorless mode using the counter electromotive force, the rotation speed of the DC motor 30 may be more than 22 rpm. In general, the counter electromotive force constant is almost the same as the above example. The method and apparatus for driving a brushless three-phase DC motor according to the present invention are related to a novel driving method and apparatus capable of generating the above rotation speed.

5 is a cross-sectional view of the brushless three-phase DC motor. The conditions and rotation speed for switching to the sensorless mode are as described above.

4 and 5, the method for driving the brushless three-phase DC motor according to the present invention will be described in detail.

As shown in FIG. 5A, the brushless three-phase DC motor 30 has a rotor 302 located at the center thereof, and an excitation coil of three phases 30a, 30b, and 30c for driving the rotor 302. It is located around the rotor 302 at an interval of 60 degrees.

First, two phases 30a and 30b of the three-phase DC motor 30 are excited. As in the conventional brushless DC motor driving method described above, when a gate voltage is first applied to two TRs Ta + and Tb- (see FIG. 4), phases a and b of the DC motor 30 are excited. At this time, the rotor 302 sets the current direction of the excitation coil so that the rotational force is generated in a constant direction (counterclockwise in the drawing). When the two phases are excited, the rotor starts to rotate under the rotational driving force.

At a short time interval, when a second signal is applied to excite the two phases 30b, 30c 120 degrees ahead of the excited phases 30a, 30b, as shown in FIG. 5B, the rotor 302 ) Rotates while accelerating counterclockwise. At the same time, the operation mode of the DC motor 30 is switched to the sensorless mode by the operation of the automatic switching switch 70 to be described with reference to FIG. 6.

Figure 6 illustrates a drive device for a brushless three-phase DC motor according to the present invention.

As shown, the drive device of the present invention is constructed almost similarly to the conventional drive device. However, the driving device of the present invention, instead of the open-loop forced driver 409 (see FIG. 1), which is built in the control unit 40 of the conventional driving device, drives the DC motor 30 in the stopped state until switching to the sensorless mode. The initial drive unit 60 is built in.

2, 5 and 6 will be described in detail the initial driving process of the brushless DC motor according to the present invention.

As shown in FIG. 6, the initial drive unit 60 receives a drive signal from the operation control unit 50, and at the start and end of the initial drive, the input line of the inverter 20 is controlled by the initial drive unit 60. A driving signal for switching to 40 is applied to the automatic changeover switch 70. Therefore, the inverter 20 is connected to the initial drive unit 60 during the initial drive, and to the control unit 40 during the sensorless mode operation.

The initial driving unit 60 is a circuit for exciting two phases, a circuit capable of applying a current to two phases 120 degrees ahead of a phase currently in operation, and simultaneously applying this current to the sensorless mode. The circuit which switches is provided. The sensorless mode operation of the DC motor 30 is performed in the same manner as the conventional driving method. Therefore, the initial driving process will be described in detail here.

When the operator operates the brushless three-phase DC motor drive device, the operation control unit 50 generates a signal for driving the initial drive unit (60). The initial driving unit 60 applies a signal to the automatic switching switch 70 at the same time as the operation starts, thereby switching the input of the inverter 20 to be connected to the initial driving unit 60.

The initial driver 60 first outputs a gate voltage for operating two TRs, Ta + and Tb− to excite the two phases 30a and 30b. After a short time interval, the initial drive unit 60 outputs the gate voltages of Tb + and Tc- of the inverter three-phase drive circuit in order to excite the two phases 30b and 30c whose phase is 120 degrees. Accelerate 302. At the same time, the initial driving unit 60 converts the input line of the inverter 20 to be connected to the control unit 40 by applying a switching signal to the automatic switching switch 70.

The controller 40 generates an output signal of the sensorless mode operation mode from the initial operation of the drive device. When the automatic switching switch 70 is switched so that the input line of the inverter 20 is connected to the control unit 40, the rotational drive of the motor 30 by the sensor + lease mode is kept constant.

As described above, when the brushless three-phase DC motor in a stationary state is driven, it is not necessary to locate the rotor using counter electromotive force, so the starting method is simple, and the overcurrent flow by the conventional driving method is simplified. This provides protection for the DC motor and prolongs its life. In addition, the present invention can be applied to various products using a brushless DC motor, such as a washing machine, an air conditioner, a refrigerator, a VCR, and an automobile.

Claims (6)

In the method of driving a brushless three-phase DC motor, (1) exciting two of the three phases of the three phase DC motor at rest; (2) exciting two phases 120 degrees out of phase with the two excited phases; And (3) Brushless three-phase DC motor drive method comprising the step of exciting the two phases ahead of 120 degrees and switching to the sensorless mode. In a drive device for a brushless three-phase DC motor, Brushless three-phase DC motor, drive means for driving the motor in accordance with a control signal, an initial drive unit for applying a first control signal to the drive means for initially driving the motor in a stationary state, after the initial drive of the motor Brushless three-phase DC motor drive device including a control unit for applying a second control signal to the drive means for driving a motor. 3. The brushless three-phase DC motor drive device according to claim 2, wherein the initial driving unit includes a circuit for exciting two of three phases of the three-phase DC motor. 3. The brushless three-phase DC motor driving device according to claim 2, wherein the initial driving unit includes a circuit for exciting two phases of which the phase is 120 degrees and switching to a sensorless mode. 5. The brushless three-phase DC motor driving apparatus according to claim 4, wherein the circuit for switching to the sensorless mode of the initial driving unit includes an automatic switching switch which is automatically switched at the same time as the sensorless mode switching signal. 3. The brushless three-phase DC motor driving device according to claim 2, wherein the initial driving unit includes a current limiting circuit capable of preventing the flow of overcurrent.